Managing Cereal Rye in a Corn-Soybean Rotation
By Matt Rush
The Benefit of Cereal Rye as a Cover Crop
Cereal Rye is arguably the most popular species of cover crop. Its benefits, versatility, and ease of management make it a popular starting point into the use of cover crops for farmers. Some of the benefits include, but are not limited to, erosion control, increased soil organic matter, weed suppression, soil cover (which can increase water infiltration and also prevent water evaporation). Also, with higher organic matter a higher water holding capacity can be expected, as well as free N, P, K, and S, that is released by the increase in biological activity.
Cereal Rye's Relationship with Corn and Soybeans
Cereal rye can be used before both corn and soybeans, but corn responds to rye differently than soybeans. It's important to know what to expect before using cereal rye as a cover crop. Soybeans have very little response to cereal rye, making it an ideal cash crop to plant after cereal rye. Corn, on the other hand, can be stunted by cereal rye if not managed properly. Cereal rye is allelopathic, meaning that it releases chemicals that will inhibit the growth or germination of other plants. Because of this, cereal rye is often used to suppress waterhemp and other hard-to-manage weeds. The allelopathy of cereal rye has very little effect, if any, on soybeans, but it does have potential to affect corn negatively. However, with proper management corn can be very successful after a cereal rye cover crop. Cereal rye releases nutrients to corn and soybeans as the rye decomposes later in the season, giving the cash crop some late season nutrients.
How many pounds per acre should you plant?
Really, seeding rate is a matter of preference. Some farmers prefer thicker stands (100#/acre) for grazing and better weed suppression, while other farmers want only 30#/acre for a cover crop that won't pose as much risk toward corn. A standard rate for a cereal rye cover crop would be around the 50#/acre range. It also needs to be understood that the more cereal rye residue there is, the more potential negative risk there will be for the cash crop (I.e. hairpinning, allelopathy in corn). But on the flip side, the more cover crop biomass, the grower will get better erosion control, better weed suppression, and a quicker advance in the soils health, due to the addition of more carbon in the soil.
Planting Soybeans into Cereal Rye
Soybeans are very forgiving when planted into cereal rye. However, there are a few things growers need to be aware of before they plant into cereal rye. Soybeans can be planted into rye the day before or the day after herbicide application. Both practices have their own pros and cons. If the soybeans are planted the day after termination it gives the herbicide time to make its way to the root of the rye plant. The reason this is important is because the planter tends to damage rye plants without killing them. Whenever the rye plant is damaged it stops ingesting herbicide, so if the soybeans are planted the day after herbicide application the grower can be confident that all of the rye will be terminated. On the other hand, some growers will argue that it is better to spray after the soybeans have been planted. Once the rye is terminated the soil dries out much slower, since living rye intakes water from the soil, and dead rye covers the soil and keeps moisture from evaporating. Dead rye can make it hard to get into the field after a rain, so that if a grower were to spray their field of rye, and then it were to rain, the grower would have to wait longer to get into the field to plant. In conclusion to this subject, It is important to let the rye ingest the herbicide before being damaged, but dead rye residue can pose a risk of not getting the cash crop planted in time. For now, neither method has been proven to be right or wrong, and decisions are based on personal preference and experience.
The option of planting two weeks after rye termination is also practical, feasible, and encouraged just as much as the other options. That being said, a grower should plant a day or two after spraying, or wait until the plant is fully dead (about two weeks). The reason behind this is that once the cereal rye plant begins to die it becomes very "tough". This toughness creates difficulty for the planter to get through. Once the rye is completely dead it is much easier to plant through. The rule of thumb is, "you can plant in it when it's alive, you can plant in it when it's dead, just don’t plant in it when it's dying." That being said, it can be planted in when it is dying if time is a factor. It will just be more difficult and planter performance should be monitored closely.
Drills, Air seeders, and precision planters are all acceptable for planting soybeans into cereal rye, but some planters perform better than others. What is important when planting soybeans in cereal rye is that the seed has good soil-to-seed contact. Hairpinning is a big factor when planting soybeans into rye, so make sure the soybean seed is getting down into the furrow and make every effort to get it covered with soil. This may mean increasing planter down pressure and possibly increasing planting depth. GENERALLY precision planters do the best job getting the soybean seed where it needs to be.
Planting Corn into Cereal Rye
There are a few things growers should be aware of before planting corn into cereal rye. First, the allelopathy of cereal rye can suppress germination and/or growth of corn. To prevent this from being an issue growers should make sure to get the corn seeded to a depth of around 2.5 inches. That should give the corn enough time to germinate without being suppressed by the allelopathy. In the Purdue Cover Crops Field guide it states:
"If a small grain (cereal rye) is still alive in the spring and corn is the following crop, then for ease of management, terminate the cover crop at least 14 days before planting corn or when the cover crop reaches 6-8 inches tall. This will reduce the potential for negative rotation effects including allelopathy, insects, diseases, soil water deficit, and N immobilization1."
Cereal rye is a host to armyworm, which feeds on corn leaf tissue. Insecticide can be used during planting to prevent armyworm. An article by Adam J. Varenhorst, Mike W. Dunbar, and Erin W. Hodgson called, “True Armyworm, Cereal Rye Cover, and No-till: an Unfortunate Combination in 2015,” which can be found on the Practical Farmers of Iowa website explains when action should be taken against an armyworm infestation:
"For corn seedlings (VE – V2) it is recommended that treatment occur if 10% or more of the seedlings corn plants are injured and larvae that are less than ¾ inch in length are still present.
For corn that is in the 7-8 leaf stage (V7 – V8), treatment of TAW (true armyworm) should be considered when larvae are less than ¾ of an inch long, there are more than eight larvae per plant, and 25% of the leaf area has been removed.
Larvae that are less than ¾ inch in length will feed for another week, and may cause additional injury. Appropriate management of TAW can prevent yield loss, as young corn plants will quickly recover from defoliation" 2
Corn can also be affected by a lack of nitrogen in its early stages of growth. This does have the potential to reduce the corn yield but can be prevented by adding starter fertilizer.
Soybeans are ideal after a cereal rye cover crop, but with proper management corn can be very successful as well.
Midwest Cover Crop Council. “Rye (Winter).” Midwest Cover Crop Field Guide, 2nd ed., Purdue, p. 73.
Hodgson, Erin W et al. “True Armyworm, Cereal Rye Cover, and No-till: an Unfortunate Combination in 2015.” Practical Farmers of Iowa, Practical Farmers of Iowa, 11 June 2015, practicalfarmers.org/blog/2015/06/11/true-armyworm-cereal-rye-cover-and-no-till-an-unfortunate-combination-in-2015/.